State Representative Carl Sciortino, a Democrat from Medford,
plans to run for ­Edward J. Markey’s seat in Congress, which is not yet vacant, according to an announcement he posted on his Facebook page.

“I am running to continue the strong progressive leadership that the families of the Fifth District have always counted on,” Sciortino said in a statement. “I look forward to bringing my record of accomplishment to Washington to fight for our progressive values.”

First elected to the State House in 2004 at age 25, ­Sciortino was vocal in the ­effort to legalize gay marriage in Massachusetts and has crafted transgender equality legislation. Sciortino, who is openly gay, represents parts of Somerville and Medford.

He graduated from Tufts University in 2000 and has a master’s degree in public admin­istration from the ­Kennedy School of Government at Harvard University.

He is the first prominent name to announce candidacy for Markey’s seat, which will become open if Markey wins the special election in June for John Kerry’s former seat in the US Senate. The district stretches from Holliston to Revere.

Jarret Bencks can be reached at bencks.globe@gmail.com. Follow him on Twitter ­@JarretBencks.